French patent FR-2,636,720, filed by the applicant, discloses a boiler wherein desulfurization agents are injected into a specific zone, referred to as desulfurization chamber, interposed between the combustion chamber and the convective exchange heat recovery zone. The desulfurization agents used in this plant are preferably non-regeneratable calcic absorbents such as lime or limestone, or industrial residues with a high calcium carbonate content (sugar mill froth, paper mill froth, etc).
Various improvements have been brought to this type of boilers in order to increase the thermal efficiency thereof while having the highest possible efficiency for trapping sulfur oxides notably.
An improvement illustrated in French patent FR-2,671,855 consists in using absorbents referred to as <<regeneratable>> absorbents that are regenerated in a regenerator located downstream from the boiler, after the final dust separator.
This improvement, which retains the advantages of plants using non regeneratable absorbents, notably within the scope of desulfurization, also allows to substantially limit the amounts of used absorbent to be dumped, which is favourable to the quality of the environment.
Furthermore, the significant decrease in the amounts of used absorbent to be eliminated allows to envisage inerting treatments at non-prohibitive costs.
In the plant described above, it is suggested that regeneration of the absorbent can be carried out by means of a fluidized bed or possibly of a rotary furnace.
An improvement illustrated in French patent FR-2,730,424 consists in carrying out regeneration simultaneously with filtration of the used absorbent in a single reactor.
The processes described above propose using as a regeneration gas a hydrogen-containing or hydrocarbon-containing compound with a total carbon number below 10, such as hydrogen, methane, ethane, propane, isobutane and/or a mixture of said gases. Hydrogen is the most suitable regeneration gas because it induces the lowest coking of absorbent. However, supplying hydrogen to an industrial site, a refinery for example, can pose problems. In fact, hydrogen is not always available in sufficient amount in refineries, in particular when substantial conversion and hydrodesulfurization operations are carried out.
Furthermore, the aforementioned two inventions, which allow regeneration of the absorbent, require specific equipments for the regeneration stage that are costly and numerous.
The present invention allows to eliminate drawbacks and components of prior plants while keeping the same regeneration efficiency.
Regeneration of a desulfurization absorbent by means of hydrogen sulfide is also proposed in patent FR-2,587,236. No means for carrying out the reaction is however mentioned in this patent.